My mistake:

$ ./1.marshall.pl 
URL = https://api.weather.gov/icons/land/day/tsra_sct,20/tsra_sct,40?s
+ize=medium
   tsra_sct => 'Thunderstorm (medium cloud cover)'

URL = https://api.weather.gov/icons/land/day/rain_showers,30/tsra_hi,3
+0?size=medium
   tsra_hi => 'Thunderstorm (low cloud cover)'

URL = https://api.weather.gov/icons/land/night/rain_showers,30/rain_sh
+owers?size=medium
   rain_showers => 'Rain showers (high cloud cover)'

URL = https://api.weather.gov/icons/land/day/bkn?size=medium
   bkn => 'Mostly cloudy'

$
[download]